In a manufacturing process of a semiconductor device or an FPD (flat panel display), a plasma is often used in processes, e.g., etching, deposition, oxidation, sputtering and the like, in order to make a processing gas react efficiently at a relatively low temperature. Conventionally, a capacitively coupled plasma processing apparatus capable of generating a plasma of a large diameter is mainly used for a single-wafer plasma processing apparatus.
Generally, in the capacitively coupled plasma processing apparatus, an upper and a lower electrode are disposed in parallel with each other in an evacuative processing chamber, and a substrate to be processed (e.g., a semiconductor wafer, a glass substrate or the like) is mounted on the lower electrode. By applying a high frequency power (an RF power) to both electrodes, electrons accelerated by a high frequency electric field formed between the electrodes, secondary electrons emitted from the electrodes, or heated electrons collide with molecules of a processing gas to generate ions. Accordingly, a plasma of the processing gas is generated, and a required microprocessing, e.g., etching, is performed on a substrate surface by radicals or ions in the plasma.
In the etching process, there is widely used a lower dual frequency application mode in which a first RF power preferably having a relatively high frequency (generally greater than or equal to about 40 MHz) for plasma generation (RF discharge) and a second RF power preferably having a relatively low frequency (generally lower than or equal to about 13.56 MHz) for ion attraction to the substrate (bias) are simultaneously applied to a lower electrode.
Meanwhile, with increasing demands for miniaturization and high integration of devices in the semiconductor processing technique, a high efficiency, high density and low bias plasma processing is required in the capacitively coupled plasma processing apparatus. To do so, the high frequency power for plasma generation tends to be set as high as possible. Meanwhile, along with the tendency to increase the chip size and the diameter of the substrate, the plasma is required to be of a larger diameter and, therefore, a chamber (processing vessel) is scaled up accordingly.
Here, the problem is that it is difficult to get uniform plasma density within the processing space (especially in a radial direction) of the chamber. That is, if RF frequency for discharge increases, standing wave is formed within the chamber (the wave effect) or more RF waves are concentrated around the central part of the surface of an electrode (the skin effect). Roughly speaking, therefore, the density of plasma becomes non-uniform in the form of the profile with the maximum at the central part on the substrate and with the minimum at the edge part. If plasma density is not uniform on the substrate, the plasma processing may not be uniform and the manufacturing yield of devices goes down.
To that end, various electrode structures have been developed. For example, in a plasma processing apparatus described in Japanese Patent Laid-open Application No. 2004-363552 and corresponding US Patent Application Publication No. 2005-0276928, uniformity in a plasma density distribution is improved by inserting a dielectric member in a main surface of an electrode facing a processing space so that an impedance to a high frequency power emitted from the main surface of the electrode to the processing space increases at a central portion of the electrode and decreases at an edge portion of the electrode.
The technique for inserting a dielectric member in a main surface of an electrode is disadvantageous in that the impedance distribution on the main surface of the electrode is fixed by a profile and a material of the dielectric member. Accordingly, a process region where the uniformity of the plasma density distribution can be controlled is small. Further, it is not possible to flexibly cope with various processes or changes of processing conditions.
Further, there is a plasma etching apparatus employing the lower electrode dual frequency application system in which the first RF power for plasma generation (discharge) and the second RF power for ion introduction are simultaneously or overlappingly applied to a lower electrode. In the apparatus, when the lower electrode has a structure in which the dielectric is embedded to make impedance of an electrode central portion relatively higher than that of an electrode edge portion, as described above, uniformity of an electric field intensity distribution on the main surface (top side) of the lower electrode is improved for the first RF power having a relatively high frequency, while the uniformity is deteriorated for the second RF power having a relatively low frequency because the electric field intensity becomes lower in the electrode central portion than the electrode edge portion. Therefore, there is a trade-off problem, i.e., improvement of plasma density uniformity resulting in deterioration of anisotropic etching uniformity.
In view of the above, the present invention provides a capacitively coupled plasma processing apparatus capable of easily or arbitrarily controlling the plasma density distribution, and improving uniformity of the plasma processing and/or the manufacturing yield.